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previous: Randall Aiken Negative feedback trades off gain f... -- 11/4/1999 7:47 AM View Thread

Re: Advanced feedback loop questions..

11/4/1999 3:17 PM
Dave Stork
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Re: Advanced feedback loop questions..
Randy wrote:  
 
Yes, disconnecting the feedback wire will make the amp run "open-loop", meaning no negative feedback. You will find it necessary to attenuate the drive signal to the phase inverter (or between the phase inverter and output tubes) if you want the gain to remain the same.  
 
You may also be surprised at how much noisier the amp will become, in some cases.  
 
One important thing to remember is the cumulative phase shift between the stages within the feedback loop. In a typical R-C coupled arrangement, there will be some frequency at which the total phase shift is 180 degrees. The important thing is to arrange for this frequency to fall outside the design bandwidth of the amplifier.